Binocular visual function and fixational control in patients with macular disease: A review

Abstract

For normally sighted observers, the centre of the macula-the fovea-provides the sharpest vision and serves as the reference point for the oculomotor system. Typically, healthy observers have precise oculomotor control and binocular visual performance that is superior to monocular performance. These functions are disturbed in patients with macular disease who lose foveal vision. An adaptation to central vision loss is the development of a preferred retinal locus (PRL) in the functional eccentric retina, which is determined with a fixation task during monocular viewing. Macular disease often affects the two eyes unequally, but its impact on binocular function and fixational control is poorly understood. Given that patients' natural viewing condition is binocular, the aim of this article was to review current research on binocular visual function and fixational oculomotor control in macular disease. Our findings reveal that there is no overall binocular gain across a range of visual functions, although clear evidence exists for subgroups of patients who exhibit binocular summation or binocular inhibition, depending on the clinical characteristics of their two eyes. The monocular PRL of the better eye has different characteristics from that of the worse eye, but during binocular viewing the PRL of the better eye drives fixational control and may serve as the new reference position for the oculomotor system. We conclude that evaluating binocular function in patients with macular disease reveals important clinical aspects that otherwise cannot be determined solely from examining monocular functions, and can lead to better disease management and interventions.

Keywords: AMD; PRL location; binocular inhibition; binocular summation; binocular vision; central vision loss; fixation stability.

FIGURE 1

Maximum reading speed during binocular and monocular viewing with the better eye for patients with central vision loss who experienced binocular reading inhibition, equality, and summation. Error bars are ±1 SE. From Silvestri et al. © 2020 The Authors. Ophthalmic and Physiological Optics published by John Wiley and Sons Ltd on behalf of College of Optometrists

FIGURE 2

Monocular preferred retinal locus (PRLs) recorded with the microperimeter and binocular PRLs estimated from the eye‐tracker recordings. Left panel shows that the locations of the PRLs were in the same location during monocular and binocular viewing conditions. Right panel shows that the monocular PRL in the worse eye changes location during binocular viewing. From Tarita‐Nistor et al.

FIGURE 3

Means (SE) of fixation stability recorded with the MP‐1 microperimeter and the EyeLink (binocular and better eye viewing [n = 20] and worse eye viewing [n = 15]). From Tarita‐Nistor et al. The Association for Research in Vision and Ophthalmology is the copyright holder of these figures

FIGURE 4

Loss of oculomotor control from binocular to monocular viewing with the worse eye, after the better eye was covered. There is also drift of the better eye during the better eye viewing condition that was associated with large phoria in the covered eye. From Tarita‐Nistor et al.